1. Field of the Invention
The present invention relates to an RF (Radio Frequency) receiving apparatus and method of a mobile communication terminal capable of performing both a GPS (Global Positioning System) function and a telecommunication function.
2. Description of the Related Art
A position tracking service is a service for automatically checking and tracking a position of a mobile communication terminal on a real time basis by using propagation detecting characteristics through a base station of a telecommunication network such as a CDMA-based mobile communication network. In the CDMA (Code Division Multiple Access) network, the position tracking service is made such that a position of the mobile communication terminal is detected and tracked by using a GPS and a mobile communication network.
E911 (Emergency 911) service is an example of a position tracking service using a CDMA network wherein a position of a mobile communication terminal capable of receiving a GPS signal is checked and an emergency rescue agency, such as a fire station, is informed of the checked position.
In order to provide the E911 service, the mobile communication terminal includes an antenna and a GPS receiver available for receiving a GPS signal. A position determination entity (PDE) calculates a position of the mobile communication terminal by using information received by the GPS receiver of the mobile communication terminal.
In case of an RF receiver of a mobile communication terminal performing both a GPS function and a CDMA function, the receiver has a GPS path for a GPS RF signal and a CDMA path for a CDMA RF signal.
FIG. 1 illustrates the construction of an RF receiver of a general mobile communication terminal.
As shown in FIG. 1, the RF receiver of the general mobile communication terminal includes an antenna 5 having GPS signal frequency band characteristics and CDMA signal frequency band characteristics, a switching unit 10 for separating a GPS signal and a CDMA signal received from the antenna 5, a GPS RF matching unit 20 for performing an RF matching function of the GPS signal transmitted from the switching unit 10, a first LNA (Low Noise Amplifier) 30 for amplifying the GPS signal outputted from the GPS RF matching unit 20, a CDMA RF matching unit 40 for performing an RF matching function of the CDMA signal transmitted from the switching unit 10, and a second LNA 50 for amplifying the CDMA signal outputted from the CDMA RF matching unit 40.
As shown in FIG. 2A, the CDMA RF matching unit 40 can include condensers C1 and C2 and a coil L1.
As shown in FIG. 2B, the CDMA RF matching unit 40 can additionally include a PCB line 41 having a certain characteristic impedance value, such as 50Ω, for example.
When a position tracking service such as an E911 for a GPS ONE function is requested by a user, a mobile communication terminal searches satellites for the E911 service while performing a switching between the GPS path and the CDMA path through the switching unit 10.
After, the GPS signals including position information and satellite numbers of satellites are received by the antenna 5 of the mobile communication terminal, and then switched to the GPS path by the switching unit 10.
The mobile communication terminal calculates a pseudo-range of positions by using the GPS signals and transmits calculated pseudo-range information and position information of satellites to the PDE or a position calculating base station through the CDMA channel.
The PDE or the position calculating base station calculates a position of the mobile communication terminal by using the pseudo-range information transmitted from the mobile communication terminal and the position information of satellites, and informs an emergency rescue agency of the calculated position of the mobile communication terminal.
However, when the E911 service function of the general mobile communication terminal is operated, the RF receiver of the mobile communication terminal uses both the CDMA mode function and the GPS mode function in a hybrid form. Thus, if the power strength of a CDMA signal becomes high, the CDMA signal would affect the GPS path and cause problems. For example, receiver sensitivity of the GPS signal would be degraded and satellite search performance of the mobile communication terminal would deteriorate. Deterioration of the satellite search performance would then lead to an inaccurate calculation of user position in an emergency situation.
Thus, what is needed is an RF receiver operating in both a CDMA mode function and a GPS mode function capable of minimizing the effects of a CDMA signal on the performance of the GPS mode function.